? Concurrent with the University of Minnesota bench study, the Minnesota Department of
Transportation (Mn/DOT) constructed three test sections of RS-HMA. [16]
? In 1990, Mn/DOT paved a portion of a recreational trail in St. Paul with hot
mix asphalt incorporating 6% shingle scrap and 3% scrap tire rubber, and 9%
shingle scrap, by weight of aggregate. Both sections have performed well and
were in service as of October 1996.
? IN 1991, Mn/DOT repaved a portion of a town highway in Mayer using RSHMA
made with factory scrap shingles. The road had last been paved in
1974, and exhibited severe oxidation and longitudinal cracking. The project
consisted of a 1.5" leveling course and a 1" wearing course.
Seven different sections of the road were paved with various amounts (5% and
7%) of shingles in both the binder and wearing courses. Control sections of
conventional HMA were also constructed.
After four years of service, Mn/DOT reported no discernable difference
between the shingle scrap sections and the control section.
? In 1991, Scott County reconstructed a portion of County State Aid Highway
17, and RS-HMA was used in the base course on 0.5 miles of the northbound
lane. Mn/DOT reported that as of December 1995, both the shingle section
and control section were in excellent condition.
? As a result of the laboratory and field testing, Mn/DOT has a specification for salvage
material in HMA which now includes the use of up to 5% scrap shingles, by weight of
aggregate. The shingles can be felt-backed or fiberglass-backed factory scrap; no
tear-off roofing is allowed. The manufacturer must certify that the material contains no
asbestos.
Since shingle scrap is an allowable material in HMA, it is the discretion of the
contractor to use RS-HMA, and Mn/DOT is not tracking each RS-HMA project.
Because there is only one shingle manufacturer and one major shingle processor in the
state, the use of RS-HMA is limited to the area served by that particular hot mix plant.
[17]